I'm so sorry to hear that your yorkie has a liver condition...My yorkie also has a liver shunt/mvd, and I know exactly what you mean about worrying...We have been through so much, and if you have any questions, please ask. Ultrasounds are many times inconclusive especially if they're being done by someone who does not specialize in liver shunts. A doppler ultrasound may be better or possibly a portography or scintigraphy may be more definitive.
If they do find that it is an operable liver shunt, I recommend that they do a liver biopsy because many times these babies also have underlying hepatic microvascular dysplasia (HMD/MVD). Has your vet put your baby on a low, vegetarian protein diet yet? Has he/she prescribed lactulose or recommended any supplements yet? My best advice to you is to join the liver shunt/mvd group on yahoo groups:
http://pets.groups.yahoo.com/group/L...d_MVD_Support/
The people on there are extremely knowledgable and their files section has a wealth of information, including the top vets to go to for liver shunt surgery. They also have a database of all the members and where they have gone for surgery. Please join the group and post your situation, they will give you a ton of very helpful advice.
Dr. Karen Tobias is at the University of Tennessee and is one of the top liver shunt vets. She has extensive experience. There are a few others, but you can ask when you join the group.
Praying for your baby, and please ask any questions that you may have.